A gas turbine engine is typically mounted below an aircraft wing or within an aircraft tail section by a pylon. The engine is typically mounted at its forward end, at an intermediate section, and at its aft end for transmitting loads to the pylon through respective forward, thrust, and aft mounts. The loads typically include vertical loads such as the weight of the engine itself, axial loads due to the thrust generated by the engine, side loads such as those due to wind buffeting, and roll loads or torques in three planes. The mounts must also accommodate both axial and radial thermal expansion and contraction of the engine relative to the supporting pylon.
Both the forward and aft mounts are typically provided for carrying in-plane loads to the pylon, which in-plane loads are those occurring in a single axial plane extending perpendicularly outwardly from the longitudinal axis of the engine and include vertical and horizontal loads and rotary torque or moments. The thrust mount is provided for transferring the axially directed thrust loads from the engine to the pylon which are tension loads during forward propulsion of the aircraft, and compression loads which occur during the use of the engines' thrust reverser during braking of the aircraft upon landing.
The forward mount typically joins either the core engine or the fan frame outer casing to the pylon, with the latter being disposed radially outwardly of the former. A forward mount typically includes a pair of circumferentially spaced apart links pivotally joined at opposite ends thereof to the fan frame outer casing and a mounting platform fixedly joined to the pylon. These links are typically inclined generally tangentially to the outer casing and radially outwardly toward each other so that the intersection point of their respective longitudinal axes is disposed radially outwardly of the outer casing in an inverted V-shaped configuration.
The intersection point acts as a center of rotation, or pendulum pivot point, about which the forward end of the engine tends to pivot in a pendulum fashion during operation which can lead to elastic lateral deflection of the engine at the forward mount relative to the pylon. These lateral deflections must be taken into account in designing interconnections between the engine and the pylon which include, for example, customer bleed piping. A portion of compressor air from the engine is typically bled through pipes to the aircraft for conventional use therein. Since the bleed pipes are connected directly to the engine, any lateral deflection of the engine will in turn cause deflection of the bleed pipes which must be accommodated to prevent excessive stress therein. By locating the forward mount links above the fan frame outer casing, and by having outwardly inclined links with the intersection point thereof being further disposed radially outwardly from the fan frame outer casing, the pendulum-type rotation of the engine is increased which can increase the lateral deflection of the engine which must be accommodated to prevent damage to the bleed pipes.
Since the aft mount is typically located radially above the point at which the side loads act on the engine, the side loads will induce roll moments at the aft mount, and yaw moments on the engine in a horizontal plane. If the center of rotation of the pendulum-type movement of the fan frame is located radially above the support of the engine at its aft mount, then side loads on the engine will effect additional roll moment at the aft mount. Accordingly, side loads acting on the engine will effect both lateral displacement of the fan frame itself as well as induce roll moments at the aft mount which must be suitably accommodated for obtaining acceptable stresses in both the forward and aft mounts and in the bleed pipes.